1. Field of the Invention
The present invention generally relates to an optical device configured to magnify and reflect an incident light. More specifically, the present invention relates to a multi-reflecting device configured to magnify and emit the incident light in a desired direction with a more slimmed size, a backlight unit and a display device having a multi-reflecting structure configured to multi-reflect an incident light.
2. Description of the Related Art
In general, display devices have been required to be smaller and flatter and to have low power consumption. Of these display devices, a liquid crystal display controls an electric field applied to a liquid material having a dielectric anisotropy to penetrate or intercept a light, thereby displaying an image or a picture. However, the liquid crystal display, which is a light receiving element configured to control the amount of externally applied light and display the light on a screen, requires an additional light source to irradiate a light into a liquid crystal panel. The display quality of the liquid crystal display depends on performance of a backlight unit as well as the liquid crystal panel.
The backlight unit includes a side-light type backlight and a perpendicular falling type backlight depending on location of the light source.
The perpendicular falling type backlight, which includes a plurality of fluorescent lamps arranged in a line on the rear of the liquid crystal panel, irradiates a light directly into the front surface of the liquid crystal panel. Although the perpendicular falling type backlight is suitable for a large display device and has good brightness, it is difficult to obtain the uniform brightness on the whole and the backlight has large power consumption. Moreover, the liquid crystal display becomes thicker.
The side-light type backlight, which includes a pipe shape line light source, emits a light from the line light source into the whole liquid crystal panel with a light guide plate. The side-light type backlight has lower power consumption and better light efficiency than those of the perpendicular falling type backlight.
FIG. 1 is a cross-sectional diagram illustrating a general backlight unit having a side-light type.
The general backlight unit of FIG. 1 includes a fluorescent lamp 1 configured to radiate a white light, a light guide plate 2 configured to supply the light radiated from the fluorescent lamp 1 to the front surface of a liquid crystal panel 8, a reflecting plate 3 configured to reflect a light streamed into the rear surface of the light guide plate 2, a diffusion plate 4 configured to diffuse the light supplied from the light guide plate 2 to improve the brightness of the light, prism sheets 5 and 6 configured to concentrate the light penetrated through the diffusion plate 4 to improve an angle of a field, and a protective sheet 7 configured to protect the prism sheets 5 and 6.
The light radiated from the fluorescent lamp 1 that is a light source is incident upon the light guide plate 2. The incident light is reflected or refracted on the front and back surface of the light guide plate 2, or reflected by the reflection plate 3 and emitted into the diffusion plate 4. The angle of the reflecting plate is so small that the incident light from the side cannot be reflected at 90° to its progress direction. As a result, the conventional backlight unit scattered-reflects the light using patterns formed on the surface of the reflecting plate 3. The prism sheet 5 and 6 concentrates the scattered-reflected light onto the front surface. That is, the prism sheets 5 and 6, arranged in length and width, concentrates the direction of the scattered-reflected light onto the front surface. The light concentrated by the prism sheets 5 and 6 is embodied into a screen depending on control of color signals of the liquid crystal panel 8.
When patterns are formed in the reflecting plate 3, the patterns result in loss of the light, so that the brightness of about 10% is used. Furthermore, the diffusion plate 4 and the prism sheets 5, 6 are additionally required in order to change the progress direction of the light into the front surface of the screen. As a result, the whole manufacturing cost of the display device is increased, implemental reliability is degraded, and the device is prevented from being thinner or lighter.
Of display devices, a projection television has been widely used which can embody a large screen with low cost. The projection television generates an image with an image generating unit including a small-sized cathode ray tube (CRT) or a liquid crystal display (LCD) as an image source, and magnifies and projects the image into a large screen through a projection lens.
FIG. 2 is a diagram illustrating a general projection television having a backside projection type.
The conventional projection television having a backside projection type includes a rectangular box-type cabinet 15 where an image generating unit 11 configured to generate an image light like a cathode ray tube or a liquid crystal display and a projection lens unit 12 configured to magnify and project the image light emitted from the image generating unit 11 are built therein. A path of the image light magnified and projected by the projection lens unit 12 is changed by a reflecting mirror 13 mounted slantingly on the rear of the cabinet 15. The image light whose light path has been changed is projected into a screen 14 mounted on the front of the cabinet 15 so that an image is displayed.
The projection television is cheaper than a LCD TV or PDP TV, and facilitates embodiment of a large screen to satisfy desire of consumers who wants a large screen. However, a proper distance between the image generating unit 11 for generating an image light and the screen 14 is required so as to secure a space where the image light proceeds for magnifying the image. As a result, the projection television has become thicker and larger.